The invention relates to a process for the preparation of storage-stable granules, in particular dyestuff granules, which are readily dispersible or are soluble in water, by build-up granulation.
It is already known (compare German Pat. No. A-2,716,478=British Pat. No. 1,567,734) that dyestuff granules can be produced by spraying an aqueous dyestuff solution into a fluidized bed of dyestuff particles.
It has furthermore been disclosed (compare German Pat. No. A-2,844,710=British Pat. No. 1,511,746) that granules can be produced by treatment of powdered pigments with granulating auxiliaries in a fluidized bed.
European Pat. No. A-24,654 proposes spraying aqueous formulations of reactive dyestuffs onto a fluidized bed, a similar technique for water-insoluble dyestuffs already having been described in German Pat. No. A-2,263,968.
However, the processes mentioned have the disadvantage that they necessitate high residence times and require large, expensive apparatuses to achieve high tonnages.
Finally, it is generally known (compare Chemie-Technik 6, 277) that granules can be produced by granulation in positive mixers, such as, for example, plough blade mixers, and subsequent drying in a fluidized bed. Nevertheless, these discontinuous processes are a method of preparing granules of low stability which are not abrasion-resistant and are used for further processing to tablets.